The invention relates to threads or fibres of polytetrafluorethylene with improved heat conductibility, as well as a method of producing the same, and a sealing packing.
Threads of polytetrafluorethylene are customarily produced in a matrix-spinning or paste extrusion procedure, in which fine-particle polytetrafluorethylene is suspended in a viscose and is spun together with the same. After spinning the threads are subjected to a thermal treatment, in which the matrix disintegrates and the polytetrafluorethylene fibres sinter together.
According to another known method threads of polytetrafluorethylene can be produced from a cylinder of the material fastened to a turning lathe and rotated relative to a cutting tool. As a result a curtain of parallel threads is pealed off and, if desired, stretched under heating. The threads produced according to this method are marked by uniform individual titres and high firmness.
It has been known to mix threads or fibres of polytetrafluorethylene with asbestos fibres, to interlace the mixture in order to form sealing packages and, if desired, to subject the latter to an post interlace treatment with an aqueous polytetrafluorethylene dispersion as well as with antifriction agents. These packages mixed of polytetrafluorethylene and asbestos are, however, poor heat conductors, thus being limited in their application. Particularly in application fields where machine parts are working at high speed and high pressure, the poor heat conductibility of the packages results in a hardening and destruction of the packages, the machine parts thus being damaged.
Many experiments have been made to improve the heat conductibility of threads of polytetrafluorethylene. An attempt was made, for instance, when producing the threads, to add heat conducting pigments, such as soot, to the polytetrafluorethylene pastes and to spin them together with the pastes. These experiments were not very successful. Pigment containing threads produced in the paste extrusion method did not show a remarkable improvement in the heat conductibility.